In a conventional wireless communication system, a technology called DRX (Discontinuous Reception) has been adopted as an example of a technology for realizing low power consumption.
DRX is a technology for realizing a power saving mode of a mobile station. Specifically, an interval involving monitoring of a PDCCH (Physical Downlink Control Channel) that controls data transmission and reception and an interval that does not involve the monitoring are defined to realize low power consumption of the mobile station. Periodic repetition of the intervals is called a DRX cycle. The mobile station does not perform signal processing, such as data processing, in the interval in which nothing is received by the PDCCH, and therefore enters the power saving mode. For example, signal processing in a baseband unit of the mobile station is temporarily suspended. However, it is difficult to completely stop the baseband unit during the power saving mode. Certain specifications, such as radio measurements, are defined even in the power saving mode; therefore, the mobile station performs minimum signal processing to comply with the specifications. The DRX cycle is configured when a base station notifies the mobile station by RRC (Radio Resource Control) at the start of communication.
A case will be explained below that DRX is performed in carrier aggregation based on LTE (Long Term Evolution) Rel-10.
First, a case (first conventional technology) will be explained below that the mobile station controls DRX in an SCell (Secondary Cell) in conjunction with the DRX cycle configuration in a PCell (Primary Cell). For example, when the PCell performs a large amount of data communication and the SCell performs SPS (Semi-persistent Scheduling) communication, an interval that does not involve the monitoring of a PDCCH is configured as a power saving mode in the PCell. In the SCell, because the SCell operates in conjunction with the DRX cycle configuration in the PCell, the same interval of the power saving mode as that of the PCell is set.
Next, a case (second conventional technology) will be explained below that DRX is individually controlled for each of component carries in the carrier aggregation. In this case, DRX in the PCell is controlled according to a traffic pattern of the PCell, and DRX in the SCell is controlled according to a traffic pattern of the SCell. Namely, an interval of the power saving mode is individually set in the PCell and the SCell. As to the examples of conventional technologies, see 3GPP TS 36.133, “Requirements for support of radio resource management”, V 9.4.0, Release 9, June 2010, for example.
However, in the first conventional technology, because the interval of the power saving mode in the SCell is set in conjunction with the PCell, if the PCell is in the interval of the power saving mode, even when the SCell does not perform SPS communication, the mobile station is caused to monitor a PDCCH. Therefore, there is a problem that electric power is wasted.
Furthermore, in the second conventional technology, because certain specifications, such as wireless measurements, are defined even in the power saving mode, minimum signal processing is performed to comply with the specifications. Therefore, there is a problem that the SCell is caused to monitor a PDCCH and a PDSCH even when DRX is individually controlled for each of the carriers.